The present invention relates to rubber bonded to metal inserts, and, more particularly, the present invention relates to an apparatus and a method for testing the shear strength of rubber bonded to a metal insert in a valve seal.
Check valves are an integral part of countless pieces of equipment in the railroad industry. Valve seals are an integral part of check valves. Valve seals are commonly made of rubber with a metal insert bonded to the rubber. The insert provides the strength while the rubber provides a seal.
It is important to know the shear strength of the rubber that is bonded to the metal insert. If the bond is not strong enough the rubber can be sheared away from the metal during a sealing operation and valve seal cannot perform its function.
Existing technology and all of the ASTM tests that are presently available do not provide an accurate measurement of the shear strength of the rubber bonded to a metal insert in valve seals. One of the major problems is that the existing technology, while excellent for many applications, does not give an accurate reading where the surface area that is being measured is small as it is in valve seals of check valves.
Therefore, the present invention provides an apparatus for measuring a shear strength of rubber bonded to a metal insert in a valve seal. The apparatus comprises an upper fixture and a radially opposed lower fixture. At least one of the upper fixture and lower fixture being movable in a longitudinal direction with respect to one another.
There is a mounting device disposed in one of the lower fixture and upper fixture of the apparatus for retaining such valve seal. A shearing means is disposed in an opposing one of the upper fixture and the lower fixture of apparatus for shearing such rubber bonded to such metal insert in the valve seal. The shearing means has an arcuate edge for contacting the valve seal closely adjacent an interface between such rubber and such metal insert.
A first means that is engageable with the shearing means controls movement of the shearing means in one of a direction for shearing the valve seal and an opposite direction for returning the shearing means to its starting position. There is further a second means that is in communication with the first means for recording such movement of the shearing means and for recording the force that is applied by the first means until such bond between such rubber and such metal insert of the valve seal is broken.
Another embodiment of the invention provides a method for testing the shear strength of rubber bonded to a metallic insert. The method comprises a first step of selecting a valve seal to be tested, followed by mounting the valve seal, that was selected in the previous step, in one of an upper and a lower fixture of a test apparatus.
A shearing means, disposed in an opposite one of the upper fixture and lower fixture of said test apparatus, is moved in a shearing direction by applying a force to the opposite one of the upper fixture and the lower fixture. Such movement is continued in the shearing direction of the opposite one of the upper fixture and the lower fixture of said test apparatus until a bond between such rubber and such metallic insert is broken.
There is a step in which the total movement of the opposite one of the upper fixture and the lower fixture of the test apparatus is measured, in a predetermined unit of distance. Such measurement further includes measuring, in a predetermined unit of force, the total force applied to the opposite one of upper fixture and lower fixture of test apparatus that is required to break such bond between such rubber and such metallic insert.
There is a step of recording such total movement of the opposite one of the upper fixture and the lower fixture of the test apparatus and such total force applied to the opposite one of the upper fixture and the lower fixture of said test apparatus that was measured in a previous step. Such movement and such force is plotted on a graph.
It is one of the primary objects of the present invention to provide an apparatus for testing the shear strength of rubber bonded to a metal insert in a valve seal.
It is also an object of the present invention to provide an apparatus which can perform a reliable test on a small surface area.
Another object of the present invention is to provide an apparatus which will provide a printed record of force required to break the bond between the rubber and the metal.
It is yet another object of the present invention to provide a method for testing the shear strength of rubber bonded to a metal insert.
In addition to the numerous objects and advantages of the present invention which have been described with some degree of particularity above, it should be both noted and understood that a number of other important objects and advantages of the lighting system will become more readily apparent to those persons who are skilled in the relevant art from the following more detailed description of the invention, particularly, when such detailed description is taken in conjunction with the appended claims.